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<title>Options for POSIX Extended Regular Expressions</title>
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<div class="titlepage"><div><div><h4 class="title">
<a name="boost_regex.ref.syntax_option_type.syntax_option_type_extended"></a><a class="link" href="syntax_option_type_extended.html" title="Options for POSIX Extended Regular Expressions">Options
        for POSIX Extended Regular Expressions</a>
</h4></div></div></div>
<p>
          Exactly one of the following must always be set for <a class="link" href="../../syntax/basic_extended.html" title="POSIX Extended Regular Expression Syntax">POSIX
          extended regular expressions</a>:
        </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                  <p>
                    Element
                  </p>
                </th>
<th>
                  <p>
                    Standardized
                  </p>
                </th>
<th>
                  <p>
                    Effect when set
                  </p>
                </th>
</tr></thead>
<tbody>
<tr>
<td>
                  <p>
                    extended
                  </p>
                </td>
<td>
                  <p>
                    Yes
                  </p>
                </td>
<td>
                  <p>
                    Specifies that the grammar recognized by the regular expression
                    engine is the same as that used by POSIX extended regular expressions
                    in IEEE Std 1003.1-2001, Portable Operating System Interface
                    (POSIX ), Base Definitions and Headers, Section 9, Regular Expressions
                    (FWD.1).
                  </p>
                  <p>
                    Refer to the <a class="link" href="../../syntax/basic_extended.html" title="POSIX Extended Regular Expression Syntax">POSIX
                    extended regular expression guide</a> for more information.
                  </p>
                  <p>
                    In addition some perl-style escape sequences are supported (The
                    POSIX standard specifies that only "special" characters
                    may be escaped, all other escape sequences result in undefined
                    behavior).
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    egrep
                  </p>
                </td>
<td>
                  <p>
                    Yes
                  </p>
                </td>
<td>
                  <p>
                    Specifies that the grammar recognized by the regular expression
                    engine is the same as that used by POSIX utility grep when given
                    the -E option in IEEE Std 1003.1-2001, Portable Operating System
                    Interface (POSIX ), Shells and Utilities, Section 4, Utilities,
                    grep (FWD.1).
                  </p>
                  <p>
                    That is to say, the same as <a class="link" href="../../syntax/basic_extended.html" title="POSIX Extended Regular Expression Syntax">POSIX
                    extended syntax</a>, but with the newline character acting
                    as an alternation character in addition to "|".
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    awk
                  </p>
                </td>
<td>
                  <p>
                    Yes
                  </p>
                </td>
<td>
                  <p>
                    Specifies that the grammar recognized by the regular expression
                    engine is the same as that used by POSIX utility awk in IEEE
                    Std 1003.1-2001, Portable Operating System Interface (POSIX ),
                    Shells and Utilities, Section 4, awk (FWD.1).
                  </p>
                  <p>
                    That is to say: the same as <a class="link" href="../../syntax/basic_extended.html" title="POSIX Extended Regular Expression Syntax">POSIX
                    extended syntax</a>, but with escape sequences in character
                    classes permitted.
                  </p>
                  <p>
                    In addition some perl-style escape sequences are supported (actually
                    the awk syntax only requires \a \b \t \v \f \n and \r to be recognised,
                    all other Perl-style escape sequences invoke undefined behavior
                    according to the POSIX standard, but are in fact recognised by
                    Boost.Regex).
                  </p>
                </td>
</tr>
</tbody>
</table></div>
<p>
          The following options may also be set when using POSIX extended regular
          expressions:
        </p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                  <p>
                    Element
                  </p>
                </th>
<th>
                  <p>
                    Standardized
                  </p>
                </th>
<th>
                  <p>
                    Effect when set
                  </p>
                </th>
</tr></thead>
<tbody>
<tr>
<td>
                  <p>
                    icase
                  </p>
                </td>
<td>
                  <p>
                    Yes
                  </p>
                </td>
<td>
                  <p>
                    Specifies that matching of regular expressions against a character
                    container sequence shall be performed without regard to case.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    nosubs
                  </p>
                </td>
<td>
                  <p>
                    Yes
                  </p>
                </td>
<td>
                  <p>
                    Specifies that when a regular expression is matched against a
                    character container sequence, then no sub-expression matches
                    are to be stored in the supplied <a class="link" href="../match_results.html" title="match_results"><code class="computeroutput"><span class="identifier">match_results</span></code></a> structure.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    optimize
                  </p>
                </td>
<td>
                  <p>
                    Yes
                  </p>
                </td>
<td>
                  <p>
                    Specifies that the regular expression engine should pay more
                    attention to the speed with which regular expressions are matched,
                    and less to the speed with which regular expression objects are
                    constructed. Otherwise it has no detectable effect on the program
                    output. This currently has no effect for Boost.Regex.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    collate
                  </p>
                </td>
<td>
                  <p>
                    Yes
                  </p>
                </td>
<td>
                  <p>
                    Specifies that character ranges of the form <code class="computeroutput"><span class="special">[</span><span class="identifier">a</span><span class="special">-</span><span class="identifier">b</span><span class="special">]</span></code>
                    should be locale sensitive. This bit is on by default for POSIX-Extended
                    regular expressions, but can be unset to force ranges to be compared
                    by code point only.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    newline_alt
                  </p>
                </td>
<td>
                  <p>
                    No
                  </p>
                </td>
<td>
                  <p>
                    Specifies that the \n character has the same effect as the alternation
                    operator |. Allows newline separated lists to be used as a list
                    of alternatives.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    no_escape_in_lists
                  </p>
                </td>
<td>
                  <p>
                    No
                  </p>
                </td>
<td>
                  <p>
                    When set this makes the escape character ordinary inside lists,
                    so that <code class="computeroutput"><span class="special">[\</span><span class="identifier">b</span><span class="special">]</span></code> would match either '\' or 'b'.
                    This bit is on by default for POSIX-Extended regular expressions,
                    but can be unset to force escapes to be recognised inside lists.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    no_bk_refs
                  </p>
                </td>
<td>
                  <p>
                    No
                  </p>
                </td>
<td>
                  <p>
                    When set then backreferences are disabled. This bit is on by
                    default for POSIX-Extended regular expressions, but can be unset
                    to support for backreferences on.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    no_except
                  </p>
                </td>
<td>
                  <p>
                    No
                  </p>
                </td>
<td>
                  <p>
                    Prevents <a class="link" href="../basic_regex.html" title="basic_regex"><code class="computeroutput"><span class="identifier">basic_regex</span></code></a> from throwing
                    an exception when an invalid expression is encountered.
                  </p>
                </td>
</tr>
<tr>
<td>
                  <p>
                    save_subexpression_location
                  </p>
                </td>
<td>
                  <p>
                    No
                  </p>
                </td>
<td>
                  <p>
                    When set then the locations of individual sub-expressions within
                    the <span class="emphasis"><em>original regular expression string</em></span> can
                    be accessed via the <a class="link" href="../basic_regex.html#boost_regex.basic_regex.subexpression"><code class="computeroutput"><span class="identifier">subexpression</span><span class="special">()</span></code></a>
                    member function of <code class="computeroutput"><span class="identifier">basic_regex</span></code>.
                  </p>
                </td>
</tr>
</tbody>
</table></div>
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        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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